Process for producing rutile TiO2

ABSTRACT

A process for preparing rutile TiO 2  by a process comprising oxidizing with oxygen or an oxygen containing gas, a mixture TiCl 4  and AlCl 3  and after at least 80% of the TiCl 4  has been converted to TiO 2  adding sufficient PCl 3  to form from 0.1-0.5% P 2  O 5  in the TiO 2 , the amount of AlCl 3  being sufficient to form 0.1-1.5% Al 2  O 3  in the TiO 2 .

DESCRIPTION TECHNICAL FIELD

The present invention relates to a process for preparing titanium dioxide from titanium tetrachloride, aluminum trichloride and phosphorous trichloride by oxidation. More specifically, the process of the present invention relates to preparing titanium dioxide by oxidation of titanium tetrachloride in the presence of aluminum chloride followed by the addition of phosphorous trichloride when the conversion to titanium dioxide is at least 80%.

BACKGROUND ART

It is disclosed in U.S. Pat. No. 3,547,671 that titanium tetrachloride can be oxidized in the presence of aluminum trichloride and phosphorous trichloride to give rutile titanium dioxide. The amount of AlCl₃ was sufficient to form 2-4% Al₂ O₃ and the amount of PCl₃ was sufficient to form from 0.5-3% P₂ O₅ based on the weight of TiO₂ pigment formed. It is also disclosed that rutilization is impeded by PCl₃ but that the effect of PCl₃ may be compensated for by increasing the AlCl₃.

DISCLOSURE OF THE INVENTION

Now a process has been found for preparing titanium dioxide substantially in the rutile form. The present invention provides for obtaining a higher rutile TiO₂ at any given level of AlCl₃ within the scope of the invention as compared to simultaneous addition of AlCl₃ and PCl₃ at one point in the reaction. The process of this invention comprises the oxidation of TiCl₄, in the presence of AlCl₃, with the later introduction into the oxidation of PCl₃, when at least 80% of the TiCl₄ is converted to TiO₂.

Accordingly, in a process for manufacturing rutile titanium dioxide by reacting TiCl₄ and oxygen or a gas containing oxygen in a reaction chamber in the presence of AlCl₃ and PCl₃ wherein the AlCl₃ and PCl₃ are added together and the amount of AlCl₃ is sufficient to form 2-4% Al₂ O₃ in the TiO₂ and the amount of PCl₃ is sufficient to form 0.5-3% P₂ O₅ in the TiO₂, the improvement has been found, wherein rutile titanium dioxide is prepared, comprising adding sufficient PCl₃ to form 0.1-0.5% P₂ O₅ in the TiO₂ separately at a later point in the reaction than when AlCl₃ is added where the TiCl₄ is at least 80% converted to TiO₂, said AlCl₃ being present in an amount sufficient to form 0.1-1.5% Al₂ O₃ in the TiO₂.

The oxidation is conducted in the presence of oxygen or a gas containing oxygen. The oxygen or gas containing oxygen is preheated to a temperature of 800°-1600° C. and then introduced into a reaction chamber of a metal pipeline-type reactor. The temperature in the reactor of the combined oxidizing gas stream and TiCl₄ /AlCl₃ can range rather widely. Generally, the temperature ranges from 1000°-1500° C.

Aluminum trichloride is added with the titanium tetrachloride in such a manner that the aluminum trichloride and titanium tetrachloride are uniformly distributed into the reactor space so that more efficient contact with preheated oxygen occurs. The aluminum trichloride and titanium tetrachloride are mixed and then sprayed concentrically in the vapor state into the reactor. Rapid, efficient mixing of the TiCl₄ /AlCl₃ can be accomplished by the use of an annular ring with outlets and side tee mixing as taught in U.S. Pat. No. 2,791,490.

The amount of aluminum trichloride that can be added is sufficient to form 0.1-1.5% Al₂ O₃ based on the TiO₂ pigment. Amounts of AlCl₃ that will form less than 0.1% will give optical values for the product TiO₂ that are lower to the point of making a less efficient pigment. Amounts of AlCl₃ that will form more than 1.5 Al₂ O₃ offer no advantage. Minimization of the AlCl₃ reduces corrosion of the metallic reactor. However, AlCl₃ is essential in the formation of rutile TiO₂. Corrosion of the metallic reactor that results with oxidation in the presence of AlCl₃, PCl₃, TiCl₄ is greatly reduced by the present invention.

Phosphorous trichloride is added to the reactor at a point in the oxidation reaction where at least 80%, preferably 88-98%, most preferably 90-94%, of the TiCl₄ introduced into the reactor has been converted to TiO₂. In a pipeline-type reactor the addition point of PCl₃ will vary depending on the size of the reactor and the particular target conversion level. It was determined that in a 10-inch inside diameter tubular reactor with oxygen at 980° C. and operating at a rate of 7830 kg of oxygen per hour with sufficient Al₂ O₃ to provide 1% Al₂ O₃ in the TiO₂ that at a point 5 feet from the entrance of the TiCl₄ a conversion of 92% of the TiCl₄ to TiO₂ had occurred.

The reaction initiated is an exothermic type. Therefore, the temperature in the reactor is at least 800° C. and ranges from 800°-1500° C. and preferably 1100°-1500° C. The addition of the PCl₃ after the achievement of at least 80% conversion to TiO₂ results in the need for less AlCl₃ to achieve the levels of rutilization achieved by this invention. Thus, the present invention offers better control of rutilization. The percent rutile in the product TiO₂ achieved by this invention is from 85-100%, preferably 92-100% and most preferably 98-100%. The present process produces more rutile at a given level of AlCl₃ than does the process where the addition of AlCl₃ and PCl₃ at the same point in the reaction. Percent rutile is determined by X-ray diffraction as is well known in the art.

Thus, the present invention results in better control of rutilization and reduced corrosion of the metallic reactor through reduced levels of AlCl₃ with the capability of achieving essentially complete rutilization. What is meant by essentially complete rutilization is 98-100%.

The amount of PCl₃ that is added in the process of this invention is sufficient to form 0.1-0.5% P₂ O₅, preferably 0.1-0.3% P₂ O₅ in the TiO₂. Amounts of PCl₃ that will form less than 0.1% P₂ O₅ result in lower optical values for the TiO₂. Amounts of PCl₃ that will form more than 0.5% P₂ O₅ give no advantage. When PCl₂ is added with AlCl₃ and TiCl₄, the rutilization, among other things, is effected. More AlCl₃ is therefore required. However, when PCl₃ is added after the TiCl₄ /AlCl₃ addition and after at least 80% of the TiCl₄ is converted to TiO₂, the PCl₃ does not substantially affect the rutilization and therefore less AlCl₃ is required to achieve a given rutilization.

The process of this invention also results in a reduction in the viscosity of a slurry of the TiO₂ in the processing of the TiO₂ product. The TiO₂ resulting from the oxidation reaction of this invention is in a semi-finished state. In order to prepare the TiO₂ for use in paper and board applications, a slurry is prepared as is illustrated in Example 3 below. In paint and plastics use the TiO₂ is wet treated, washed and milled to a dry powder.

EXAMPLES

In the examples that follow all percentages and parts are by weight unless otherwise indicated.

EXAMPLE 1--(BEST MODE)

A stream of oxygen preheated to a temperature of 980° C. was introduced into one end of a 10-inch inside diameter tubular, chlorine purged reactor operated at 1.76 kg/cm² gauge at a rate of 7730 kg per hour.

A titanium tetrachloride stream containing sufficient aluminum trichloride to provide one percent Al₂ O₃ in the titanium dioxide based on the titanium dioxide was preheated to 480° C. and introduced into the reactor in vapor form through an annular ring and mixing tee to insure complete and uniform mixing with the preheated oxygen.

The temperature of the reaction gas stream was 1300°-1450° C. after the addition of the titanium tetrachloride and aluminum trichloride is complete. PCl₃ is then added at a point where 92% of the TiCl₄ was converted to TiO₂ through a similar annular ring in sufficient quantity to provide 0.25% P₂ O₅ on the titanium dioxide. The PCl₃ addition was followed by scrub solids before the reaction stream exited the reactor into cooling ducts. The reaction stream with the scrub solids was cooled. The reaction produced pigmentary size 100% rutile TiO₂.

Scrub solids are rutile TiO₂ of granular 20-40 mesh size that has been calcined and was used to clean the walls of the reactor.

COMPARATIVE EXAMPLE A

Rutile TiO₂ was prepared by the process of Example 1 except that sufficient AlCl₃ was added to form 1% Al₂ O₃ in the TiO₂ and no PCl₃ was added.

COMPARATIVE EXAMPLE B

Rutile TiO₂ was prepared by the process of Example 1 except that PCl₃ was added with the TiCl₄ and AlCl₃ and the amount of AlCl₃ and PCl₃ was sufficient to form 1% Al₂ O₃ and 0.25% P₂ O₅ respectively in the TiO₂.

COMPARATIVE EXAMPLE C

Rutile TiO₂ was prepared by the process of Example 1 except that sufficient AlCl₃ was added to form 1.5% Al₂ O₃ and sufficient PCl₃ was added with the AlCl₃ to form 0.25% P₂ O₅.

EXAMPLE 2

Rutile TiO₂ was prepared by the process of Example 1 except that sufficient AlCl₃ and PCl₃ was added to form 1% Al₂ O₃ and 0.57% P₂ O₅ respectively.

EXAMPLE 3

The TiO₂ prepared by Examples 1 and 2 and Comparative Examples A, B and C was made into a rutile pigment slurry by the process described below and the data obtained is shown in the table that follows:

682 kg of H₂ O were added to a grind tank. Add 10.9 kg of powdered tetrapotassium pyrophosphate and 16.4 kg of liquid 2-amino-2-methyl-1-propanol (AMP) were added to the H₂ O and stirred until dissolved. 2730 kg of TiO₂ prepared as described above were added over a period of 20 minutes to form a slurry. The slurry (80% solids) was ground for 30 minutes. The slurry contents were diluted to ˜72% by adding 409 kg of H₂ O. The slurry was screened to remove grit. Samples were evaluated for optical value (blue green brightness) in a typical board coating formula.

    ______________________________________                                         BOARD COATING EVALUATION                                                                              Optical Value                                           Example No.                                                                             % Solids  Rutile   Viscosity                                                                             Blue  Green                                 ______________________________________                                         Comparative                                                                             72.5      99       1200   85    85                                    Example A                                                                      Comparative                                                                             72.4      95       600    102   102                                   Example B                                                                      Comparative                                                                             72.5      98-99    600    103   101                                   Example C                                                                      1        71.9      99       630    102   101                                   2        72.2      99       460    99    97                                    ______________________________________                                    

EXAMPLE 4 (Evaluation in Enamel Grade Pigment)

The process described in Example 1 was followed except that sufficient PCl₃ and AlCl₃ was added to form the percent P₂ O₅ and percent Al₂ O₃ shown below to prepare TiO₂. For this process, 4000 grams of TiO₂ was placed in 10 liters of water and the slurry that resulted was heated to 60° C. Fifty percent NaOH was added to bring the pH to 9.0. Three hundred twenty cc of a sodium aluminate solution (375 g Al₂ O₃ /liter) and enough 20% HCl solution to maintain the pH at 9.0 was added. The pH was adjusted to 8.2 with 20% HCl. The slurry was digested for 30 minutes at 60° C., filtered, washed to 7000 ohms and dried at 140° C. for 48 hours. The dry powder was divided into four equal parts and ground in a fluid energy mill at rates of 350 g/min, 650 g/min, 1100 g/min and 2200 g/min. The pigment samples are evaluated in a high gloss alkyd enamel.

    ______________________________________                                         ALKYD ENAMEL EVALUATION                                                        Sample          Rate          Gloss                                            ______________________________________                                         Enamel grade     650 g/min    79                                               0.25% P.sub.2 O.sub.5                                                                          1100 g/min    79                                               1.0% Al.sub.2 O.sub.3                                                                          2200 g/min    75                                               Enamel grade     650 g/min    79                                               0.46% P.sub.2 O.sub.5                                                                          1100 g/min    78                                               1.0% Al.sub.2 O.sub.3                                                                          2200 g/min    77                                               ______________________________________                                    

EXAMPLE 5 (Evaluation in Plastic Grade)

The process of Example 1 was followed except that sufficient PCl₃ and AlCl₃ was added to form the P₂ O₅ and Al₂ O₃ shown below to prepare TiO₂. Four thousand grams of this TiO₂ were dispersed in 2000 ml of H₂ O and diluted to 10,000 ml of solution by adding H₂ O. The contents were stirred and heated to 60° C. Thirty-eight ml of a sodium aluminate solution were added. (341 g Al₂ O₃ /liter.) The pH was adjusted to 8.0 with hydrochloric acid. The mixture was cured at 60° C. for 1/2 hour, filtered, washed to 7000 ohms and dried about 48 hours at 140° C. It was then screened through a 10 mesh screen and treated with a grinding aid and ground in a fluid energy mill.

Samples were also prepared by scaling the laboratory procedure that follows up to 50 tons. Samples were evaluated in polyethylene dispersed in the conventional manner.

    ______________________________________                                         POLYETHYLENE EVALUATION                                                                        Brightness                                                                              Yellow Index                                          ______________________________________                                         Lab sample 0.25% P.sub.2 O.sub.5,                                                                93.8       3.3                                               1% Al.sub.2 O.sub.3                                                            Plant sample 0.25% P.sub.2 O.sub.5,                                                              94.6       3.0                                               1% Al.sub.2 O.sub.3                                                            Plant sample 0.25% P.sub.2 O.sub.5,                                                              94.7       2.7                                               1% Al.sub.2 O.sub.3                                                            ______________________________________                                    

EXAMPLE 6 (Evaluation in Emulsion Flat Grades)

The procedure of Example 1 was followed except that sufficient PCl₃ and AlCl₃ was added to form the percent P₂ O₅ and percent Al₂ O₃ show below to prepare TiO₂.

Three thousand grams of this TiO₂ was placed in 10 liters of water and the slurry that resulted was heated to 70° C. and 30 ml of a 20% hydrochloric acid added. Five hundred thirty-eight ml of a sodium silicate solution (390 g SiO₂ /liter) were added while maintaining the pH below 7.0 with 20% hydrochloric acid. The pH was adjusted to 7.5-8.0 with 50% NaOH solution. The slurry was digested at 70° C. for 1/2 hour. Five hundred cc of a sodium aluminate solution (360 g Al₂ O₃ /liter) were added while holding the pH between 7.5 and 8.0 with 20% hydrochloric acid. The slurry was digested at 70° C. for 1/2 hour, filtered, washed to 7000 ohms and dried at 140° C. for 48 hours. It was then ground in a fluid energy mill. The samples were evaluated in interior emulsion flat paints.

    ______________________________________                                         EVALUATION                                                                     Emulsion Flat Hiding                                                                  Interior Emulsion                                                                            Interior Emulsion                                                Test Formula  Test Formula                                                     0.3 kg TiO.sub.2 /kg 48 PVC                                                                  0.2 kg TiO.sub.2 /kg 55 PVC                               Sample   HP      HPo     Stain HP    HPo   Stain                               ______________________________________                                         Flat emulsion                                                                           120     63.0    cons.sup.-                                                                           112   65    vvsl.sup.-                          grade lab                                                                      produced                                                                       0.25% P.sub.2 O.sub.5                                                          1.00% Al.sub.2 O.sub.3                                                         ______________________________________                                    

INDUSTRIAL APPLICABILITY

The process of this invention produces an essentially 100% rutile TiO₂ with less metallic corrosion in the oxidation reactor than when PCl₃ is added with TiCl₄ and AlCl₃. The 100% rutile TiO₂ made into a slurry for paper or board application displays superior optical values and lower slurry viscosities. The 100% rutile TiO₂ from oxidation is wet treated, filtered, washed, dried and fluid energy milled to form a dry TiO₂ for plastics pigmentation and for paints. 

I claim:
 1. In a process for manufacturing rutile titanium dioxide by reacting TiCl₄ and oxygen or a gas containing oxygen in a reaction chamber in the presence of AlCl₃ and PCl₃ wherein the AlCl₃ and PCl₃ are added to the reactor together, the amount of AlCl₃ is sufficient to form 2-4% Al₂ O₃ in the TiO₂ and the amount of PCl₃ is sufficient to form 0.5-3% P₂ O₅ in the TiO₂, the improvement wherein rutile TiO₂ is produced comprising adding sufficient PCl₃ to form 0.1-0.5% P₂ O₅ in the TiO₂ separately at a later point in the reactor than where AlCl₃ is added where the TiCl₄ is at least 80% converted to TiO₂, said AlCl₃ being present in an amount sufficient to form 0.1-1.5% Al₂ O₃ in the TiO₂.
 2. The improvement of claim 1 wherein the amount of PCl₃ is sufficient to form 0.1-0.3% P₂ O₅.
 3. The improvement of claim 1 wherein the TiCl₄ is 88-98% converted to TiO₂.
 4. The improvement of claim 3 wherein the rutile titanium dioxide amounts to from 92-100% as measured by X-ray diffraction.
 5. The improvement of claim 3 wherein the amount of PCl₃ is sufficient to form 0.1-0.3% P₂ O₅.
 6. The improvement of claim 1 wherein the TiCl₄ is 90-94% converted to TiO₂.
 7. The improvement of claim 6 wherein the rutile titanium dioxide amounts to from 92-100% as measured by X-ray diffraction.
 8. The improvement of claim 6 wherein the amount of PCl₃ is sufficient to form 0.1-0.3% P₂ O₅.
 9. The improvement of claim 1 wherein the rutile titanium dioxide amounts to from 92-100% as measured by X-ray diffraction.
 10. The improvement of claim 9 wherein the amount of PCl₃ is sufficient to form 0.1-0.3% P₂ O₅.
 11. The improvement of claim 1 wherein the rutile titanium dioxide amounts to from 98-100% as measured by X-ray diffraction. 